Food labels seem to provide all the information a thoughtful consumer needs, so counting calories should be simple. But things get tricky because food labels tell only half the story.
A calorie is a measure of usable energy. Food labels say how many calories a food contains. But what they don’t say is that how many calories you actually get out of your food depends on how highly processed it is.

Looks official and definitive, but it is just a part of the picture. FDA

